patch 8.1.0273: invalid memory access when using 'incsearch'

Problem:    Invalid memory access when using 'incsearch'.
Solution:   Reset "patlen" when using previous search pattern.
diff --git a/src/ex_getln.c b/src/ex_getln.c
index c2eb0a8..3fb9c86 100644
--- a/src/ex_getln.c
+++ b/src/ex_getln.c
@@ -504,7 +504,11 @@
 	return FAIL;
 
     if (firstc == ccline.cmdbuff[skiplen])
+    {
 	pat = last_search_pattern();
+	skiplen = 0;
+	patlen = STRLEN(pat);
+    }
     else
 	pat = ccline.cmdbuff + skiplen;